Certain metabolites and chemicals produced in or entering the body and bloodstream are excreted in the breath. The level in the body or blood stream may be determined by measuring it in the breath. For example, breath CO levels may be measured to detect and monitor underlying disorders such as hematological disorders and conditions, metabolic disorders, and environmental and behavioral problems. For example, end-tidal CO can be correlated to blood CO, which can be indicative of hemolysis, smoking or inhalation poisoning. In order to measure end-tidal CO, alveolar gas may be collected non-invasively from the exhaled breath of a patient by capturing the portion of the breath at the end of exhalation. The captured end-tidal gas can then be analyzed for its CO concentration thus completing the non-invasive diagnostic measurement. Typically, a correlation exists between the level of an analyte in the exhaled gas and the level of a metabolite or chemical or other substance in the body or blood, for example a 1:1 ratio or some other ratio.
It has been discovered that proper and accurate correlation of blood-to-breath analyte levels, such as CO gas, may be dependent on the breathing pattern. Typically, breath samples are taken without contemplating whether or not the patient's breathing pattern is appropriate for the diagnostic analysis being taken. When the level of a certain gas in the blood is being analyzed by measuring it in the breath, in some situations, in order for the correlation of blood-to-breath level to be accurate, the patient may need to be breathing at their normal resting tidal volume or minute volume breathing pattern in terms of frequency and depth of breathing. In other situations, the blood-to-breath correlation may be more accurate if the person performs a non-resting tidal volume breath, such as a sigh breath or breath hold (for example when attempting to diagnose a metabolic disorder), or deep breath (for example when attempting to diagnose an infection).
In addition, it may be beneficial during a breath test, that the end-tidal gas be collected automatically or semi-automatically from a non-cooperative patient or a patient incapable of following instructions. Or in some cases a patient that may be capable of cooperating, but is influenced by the test, and inadvertently may submit a sample when breathing abnormally. In these situations, obtaining a pure and adequate sample of gas from the breath can be challenging.